The present disclosure relates to a coordinate measuring machine, in particular to an optical coordinate measuring machine, having an optical sensor for optically capturing a workpiece to be measured, an illumination device for illuminating the workpiece to be measured, and a pose determination unit for determining data relating to the position and orientation of the workpiece to be measured.
An exemplary coordinate-measuring machine of this type is known for example from DE 101 40 174 A1 and DE 10 2012 103 554 A1.
Coordinate measuring machines serve for checking workpieces, for example as part of quality assurance, or for ascertaining the geometry of a workpiece as part of what is known as “reverse engineering.” Moreover, various other application possibilities are conceivable.
In coordinate measuring machines, different types of sensors may be used to capture the workpiece to be measured. By way of example, sensors that measure in tactile fashion are known in this respect, as are sold by the applicant under the name “VAST XT” or “VAST XXT”. Here, the surface of the workpiece to be measured is scanned with a stylus, the coordinates of said stylus in the measurement space being known at all times. Such a stylus may also be moved along the surface of a workpiece in a manner such that a multiplicity of measurement points can be captured at set time intervals during such a measurement process as part of a so-called “scanning method”.
It is moreover known to use optical sensors that facilitate contactless capturing of the coordinates of a workpiece. The present disclosure relates to such a coordinate measuring machine having an optical sensor. One example of such an optical sensor is the optical sensor sold by the applicant under the name “ViScan”. An optical sensor of this type can be used in various types of measurement setups or coordinate measuring machines. Examples of such coordinate measuring machines are the products “O-SELECT” and “O-INSPECT”, which are sold by the applicant.
Some examples of coordinate measuring machines, including the “O-INSPECT” just mentioned, use both an optical sensor and a tactile sensor, for example in order to be able to perform various examination tasks at a single machine and ideally with a single clamping of the workpiece to be measured. Coordinate measuring machines of this type are also referred to as multisensor coordinate measuring machines.
For an exact measurement, it is mandatory in an optical coordinate measuring machine to provide a suitable illumination of the workpiece to be measured. In addition to what is known as transmitted-light illumination, where the light source is situated, relative to the optical sensor, behind the workpiece, what is known as incident-light illumination or reflected-light illumination is typically used in order to illuminate the workpiece on its top side, which faces the optical sensor. Illumination that is adapted exactly to the workpiece is of utmost importance, in particular because it is possible to hereby improve the bright-to-dark contrast that is necessary in the optical detection of the workpiece. For this reason, the illumination must be adapted individually by the user of the coordinate measuring machine to the shape and the geometric properties of the workpiece. Matching the light setting of the illumination device in this fashion can at times take a relatively large amount of time. What should in principle also be ensured is that identical workpieces are also measured under respectively identical light conditions.
The simplest approach, specifically that of performing the light settings separately for each workpiece by hand, is highly time-consuming and prone to errors. Comparable measurements can hardly be ensured in this way. For this reason, serial measurements of a plurality of workpieces having identical construction are frequently performed with identical light settings. During this process, the light settings are optimized for the first workpiece only before the measurement thereof and are then maintained. In order to rule out a change in orientation of the subsequent workpieces relative to the illumination device, the workpieces are placed, always in the same way, into specifically provided clamping apparatuses on the measurement table of the coordinate measuring machine. However, the use of such clamping aids is costly and not practical either if the workpiece types frequently change.
Another possibility for solving the above-mentioned problem is the automated production of a plurality of predefined illumination scenarios before a new workpiece is measured and the successive examination of the contrast ratios for each illumination scenario that occur in the region of the workpiece so as to finally select the “optimum” illumination scenario for the respective workpiece. A similar optimization method for selecting the “optimum” light settings of the illumination device in coordinate measuring machines is known from DE 102 15 135 A1. However, it is to be understood that even an optimization method of this type is relatively time-consuming and likewise requires a relatively large computer-assisted computational outlay.